This invention relates to foams made by polymerizing emulsions containing functionalized metal oxide nanoparticles by both thermal and photopolymerization methods. The emulsions comprise a reactive phase and an immiscible phase wherein the reactive phase or both phases are continuous. The resulting foams may be closed or open cell, depending on the initial emulsion microstructure.
The present invention features a novel method for creating foams from water-in-oil emulsions containing functionalized metal oxide nanoparticles. The foams may be made from high internal phase emulsions (HIPEs) and other water-in-oil emulsions using one or both of a photopolymerization process or a thermal polymerization process. The foams may be made by a batch process, or a continuous process in which the emulsion may be coated on a moving support. In either case, the foam is polymerized and crosslinked by exposure to actinic radiation, by heating, or using both actinic radiation and heating. The actinic radiation polymerization process is fast, which can allow a broad range of materials to be used because the emulsion needs to be stable for only a short time (seconds to minutes). One aspect of the present invention provides a process for making a crosslinked polymeric foam comprising: a) mixing a reactive phase comprising at least one polymerizable material and at least one functionalized metal oxide nanoparticle material (for example silica nanoparticles functionalized with polymerizable groups) with at least one initiator and a fluid immiscible with the reactive phase to form an emulsion wherein the immiscible fluid forms a discontinuous or co-continuous phase with the continuous reactive phase; b) shaping the emulsion; and c) exposing the emulsion to actinic radiation or thermal energy to form a crosslinked polymeric foam containing residual immiscible fluid.
If desired, the functionalized metal oxide nanoparticle material can function as an emulsifier and /or crosslinking agent. Optionally, a separate emulsifier and crosslinking agent, in addition to the functionalized metal oxide nanoparticle material, may be added to the reactive phase.
The process may include exposing the emulsion to both actinic radiation and thermal energy, simultaneously or sequentially.
The polymerizable material may be the same as the crosslinking agent or the emulsifier.
The immiscible phase is typically water, but may comprise other fluids such as fluorocarbons or organic liquids. The immiscible fluid may comprise 74 volume percent, or more, of the emulsion.
The reactive phase may include, e.g., non-polymerizable materials and materials that can incorporate functional groups into the foam.
The structure of the foam of the present invention may be controlled by aging the emulsion prior to polymerization or by selection of a particular agitation method for making the emulsion.
The emulsion may include photoinitiators in the reactive or immiscible phase. Preferably, the photoinitiators are activated by ultraviolet or visible radiation of 300 to 800 nanometers. The emulsion may include thermal initiators in addition to, or instead of, photoinitiators. The thermal initiators can be present in either the reactive phase or the immiscible phase.
Polymerization and crosslinking of the emulsion may occur in as little as 10 minutes or even 10 seconds particularly when photopolymerization is used.
A further aspect of the invention is an emulsion having a continuous reactive phase comprising at least one polymerizable material and at least one type of functionalized metal oxide nanoparticle, a discontinuous or co-continuous phase comprising a fluid immiscible with the reactive phase, and either a photoinitiator or a thermal initiator.
Foams of the present invention may be open or closed cell. Foams of the present invention made from HIPEs have relatively homogeneous cells. The cells of the open cell foams of the present invention may be joined by open xe2x80x9cwindowsxe2x80x9d or holes connecting adjacent cells. All of the foams of the present invention contain functionalized metal oxide nanoparticles. Another aspect of the invention is a cross-linked foam comprising residue of a photoinitiator that absorbs at a wavelength of 300 to 800 nanometers. A further aspect of the invention is a crosslinked foam comprising residue of a thermal initiator. Further, foams can contain residue of both a thermal initiator and a photoinitiator.
The foams may be crosslinked within the voids of a material selected from the group consisting of polymeric, woven, nonwoven, and metals. Alternatively, the foam may contain non-polymerizable materials selected from the group consisting of polymers, metals, particles, and fibers.
Some of the foams may be able to collapse when fluid is removed.
Another aspect of the present invention is articles made using the foams of the present invention.
As used in this invention:
xe2x80x9cHIPBxe2x80x9d or xe2x80x9chigh internal phase emulsionxe2x80x9d means an emulsion comprising a continuous reactive phase, typically an oil phase, and a discontinuous or co-continuous phase immiscible with the oil phase, typically a water phase, wherein the immiscible phase comprises at least 74 volume percent of the emulsion;
xe2x80x9cwater-in-oil emulsionxe2x80x9d means an emulsion containing a continuous oil phase and a discontinuous water phase; the oil and water phases may be co-continuous in some cases;
xe2x80x9creactive phasexe2x80x9d or xe2x80x9coil phasexe2x80x9d means the continuous phase which contains the monomer or organic reactive species that are sensitive to reactive propagating species (e.g., those having free radical or cationic centers) and can be polymerized of crosslinked;
xe2x80x9cimmiscible phasexe2x80x9d means a phase in which the reactive components have limited solubility; the immiscible phase may be discontinuous, or co-continuous with the reactive phase components;
xe2x80x9cstablexe2x80x9d means the composition and microstructure of the emulsion are not changing over time;
xe2x80x9cfunctional groupxe2x80x9d means a chemical entity capable of undergoing a non-polymerization reaction;
xe2x80x9cfunctionalized metal oxide nanoparticlexe2x80x9d means a nanoparticle prepared from colloidal materials from the group of silica, zinc oxide, titania, alumina, zirconia, vanadia, chromia, iron oxide, antimony oxide, tin oxide, other colloidal metal oxides, and mixtures thereof, functionalized such that (a) the nanoparticles dissolve in the reactive and/or immiscible phase and (b) chemical entities attached to the nanoparticle are capable of polymerization; these particles can comprise essentially a single oxide such as silica or can comprise a core of an oxide of one type (or a core of a material) on which is deposited the oxide of another type;
xe2x80x9cmonomerxe2x80x9d means chemical species capable of polymerizing, it includes monomers and oligomers;
xe2x80x9creactive surfactantxe2x80x9d means a surfactant (i.e., emulsifier) having sufficient reactivity to undergo polymerization reactions such that it becomes part of a polymer backbone;
xe2x80x9copen cellxe2x80x9d means a foam wherein the majority of adjoining cells are in open communication with each other; an open cell foam includes foams made from co-continuous emulsions in which the cell structure is not clearly defined, but there are interconnected channels creating at least one open pathway through the foam;
xe2x80x9cwindowxe2x80x9d means an intercellular opening;
xe2x80x9cshapingxe2x80x9d means forming into a shape and includes pouring, coating, and dispensing;
xe2x80x9cpolymerizexe2x80x9d or xe2x80x9ccurexe2x80x9d are used interchangeably in this application and indicate a chemical reaction in which monomers, oligomers, polymers, or functionalized metal oxide nanoparticles combine, including by crosslinking, to form a chain or network;
xe2x80x9ccrosslinkingxe2x80x9d means the formation of chemical links between polymer chains;
xe2x80x9ccrosslinking agentxe2x80x9d means a material that adds to a polymer chain a site capable of forming a link to another polymer chain;
xe2x80x9ccationically curable monomerxe2x80x9d means a monomer capable of undergoing polymerization in which cationic species propagate the polymerization reaction and includes monomers containing, e.g, epoxide or vinyl ether moieties;
xe2x80x9cethylenically unsaturatedxe2x80x9d means a monomer having a carbon-carbon double bond in its molecular structure;
xe2x80x9cactinic radiationxe2x80x9d means photochemically active radiation including near infrared radiation, visible light, and ultraviolet light;
xe2x80x9cUVxe2x80x9d or xe2x80x9cultravioletxe2x80x9d means actinic radiation having a spectral output between about 200 and about 400 nanometers;
xe2x80x9cvisible lightxe2x80x9d means actinic radiation having a spectral output between about 400 to about 800 nanometers;
xe2x80x9cnear infraredxe2x80x9d means actinic radiation having a spectral output between about 800 to about 1200 nanometers;
xe2x80x9cphotoinitiatorxe2x80x9d means a chemical added to selectively absorb actinic radiation and generate reactive centers such as free radicals and cationic species;
xe2x80x9cthermal initiatorxe2x80x9d means a species only capable of efficiently inducing or causing polymerization or crosslinking upon exposure to heat;
xe2x80x9cpressure sensitive adhesivexe2x80x9d or xe2x80x9cPSAxe2x80x9d means an adhesive that will adhere to a variety of dissimilar surfaces upon mere contact without the need of more than finger or hand pressure; PSAs are sufficiently cohesive and elastic in nature so that, despite their aggressive tackiness, they can be handled with the fingers and removed from smooth surfaces with little or no residue left behind; PSAs can be quantitatively described using the xe2x80x9cDahlquist criteriaxe2x80x9d which maintains that the elastic modulus of these materials is less than 106 dynes/cm2 at room temperature. See Pocius, A. V., Adhesion and Adhesives: An Introduction, Hanser Publishers, New York, N.Y., First Edition, 1997, and
xe2x80x9cvoidxe2x80x9d means any open space, in a foam, such as holes, cells, and interstices.
An advantage of at least one embodiment of the present invention is that the resulting foams and articles made with the present invention contain functionalized metal oxide nanoparticles, which might have desirable activity.
An advantage of at least one embodiment of the present invention is that a broad spectrum of foam physical properties can be generated by manipulating the type of monomers and co-monomers, the monomer to co-monomer ratio, cell size, percentage of open cells, density of the foam, and mixing methods.
An advantage of at least one embodiment of the present invention is that the foams may be hydrophilic when produced, depending on monomer and surfactant choice. This eliminates having to incorporate hydrophilizing agents or treat the foam surfaces to make them hydrophilic (e.g., when used as an absorbent) as is required with some styrenic-based thermally polymerized foams.
An advantage of at least one embodiment of the present invention is that the foam materials are suitable for a myriad of applications such as energy and fluid absorption, insulation, and filtration. An advantage of at least one embodiment of the present invention is that multilayer articles comprising one or more foam layers may be made.
An advantage of at least one embodiment of the present invention is that the foams made by the current invention may contain no added surfactant because the functionalized metal oxide nanoparticles have some emulsifying capability. The functionalized metal oxide nanoparticles can act as a reactive surfactant. In this case, no additional surfactant is necessary in the emulsion. This aspect of the invention is further advantageous because the functionalized metal oxide nanoparticles become polymerized into the final foam structure and will have a reduced tendency to leach when the foam is used.